Consumer items made of plastic are used increasingly, for example, beverage bottles made of PET, household objects, such as, keys or similar items, or housing parts of electronic apparatuses. The worldwide spread of plastics in the greatest variety of fields has, in the meantime, reached such proportions that the raw materials are becoming rarer and thus more expensive. Recycling plastics is important not only for environmental reasons, it is also becoming more advantageous from an economic standpoint.
As raw material prices increase, the recycling methods that are of greatest interest are those that either maintain or increase the quality of the original material with regard to processability after recycling.
Originally, the assumption was that collected PET material (RPET), owing to the quality loss after recycling and different contaminations, could no longer be used in the same application (for example, beverage bottles). However, it has recently become apparent that such a use is possible. Methods exist which recycle the plastics at a qualitatively high level, to allow their reuse in the same application (for example, the food sector).
Using a method according to DE 199 53 659 A1, post-consumer PET bottles (RPET) are crushed, and first washed and surface dried in the usual way. Then the flakes are introduced into a crystallizer, in which they are heated and crystallized by a hot gas stream at 180° C. Then, the flakes reach a shaft reactor, where they are recondensed continuously for at least two hours in countercurrent flow with respect to an N2 gas stream (temperature approximately 220° C.). Then the flakes are cooled again in this continuously running process. One drawback of this method is that the PET flakes are heated in the given reactors, i.e., in the crystallizer and the shaft reactor, respectively, which requires a relatively large amount of heating energy. In addition, the heat transfer is carried out via (inert) gas, which requires a complicated preparation system for the heat transfer medium. Another disadvantage of the method is that the recondensation of the flakes is continuous. In a continuous process management, the desired IV (intrinsic viscosity) cannot be set exactly, because the heating which can be carried out is limited by process parameters (for example, temperature and time). The fact that the actual IV of the flakes to be treated can be different—for example, some flakes have an intrinsic viscosity IV of 0.70 dL/g, while others already have a value of 0.76 dL/g—is not taken into account in this procedure, so that all the flakes undergo an increase in their intrinsic viscosity in the same way (same time, same process conditions), without taking into account their original IV.
Therefore, the problem of the present disclosure is to provide a method and a device for recycling plastics, which present considerably reduced energy consumption, and in which the IV of the plastics can be set in a controlled manner.